1. Field of the Invention
The present invention relates to an organic solvent recovering system adapted to clean a soil contaminated by a contamination substance such as organic solvent and recover the solvent contaminant from the soil, and more particularly, a system for recovering the organic solvent in the soil having an improved ability for recovering the organic solvent, having a compact structure to be easily movable, generating less condensed liquid in a decantation process and having an improved energy demand.
2. Description of the Prior Art
For example, atmospheric environments or soil environments near industrial areas performing defatting working, metal cleaning working, etc., dry cleaning shops, chemical material storage and treatment areas, and chemical substance disposal areas are often contaminated by organic solvents such as trichloroethylene, tetrachloroethylene, dichloromethane and the like.
With respect to the soil environment, in the initial stage of the soil contamination caused by liquid substances, the contaminants generally exist at a ground surface area on a ground-water level. However, when the soil contamination has continuously progressed, the contaminants soak into a ground-water bed, providing a severe problem of the contamination of the ground water. Therefore, it has been desired to remove or recover the contaminants before the soaking of the contaminants to the ground-water bed.
Prior art provides various methods for removing or recovering such liquid contaminants in a soil, which includes a method in which the contaminated soil portion is excavated from the soil and the excavated soil portion is thereafter air-dried, a method in which the excavated soil portion is heated at about 1300.degree. C. by means of a heating furnace or the like, and a method in which the liquid contaminants are washed out through liquid-liquid contact or gas-liquid contact by supplying water or water vapor in the soil.
However, these prior art methods involve much labor and time for, for example, digging the soil and also provide less soil cleaning efficiency or secondary contamination problem. In order to solve such problems, the prior art further provides various cleaning systems or apparatus such as disclosed in the Japanese Patent Laid-open Publication Nos. HEI 4-225887 and HEI 5-76618.
In the prior art technologies such as disclosed in the Japanese Patent Laid-open Publication No. HEI 4-225887, proposed is to use an adsorption apparatus or a gas treating apparatus provided with an activated carbon for adsorbing and removing the volatile contaminants sucked from the contaminated soil by a vacuum pump. However, in such apparatus, the activated carbon adsorbing the volatile contaminants is not regenerated, and it is required to additionally prepare an activated carbon treating or regenerating apparatus because the activated carbon fully adsorbing the volatile contaminants, then constitutes a new contaminated material, unless treated. Still furthermore, in such apparatus, it is obliged to frequently change the activated carbon with a new one, thus being inconvenient.
Furthermore, in the Japanese Patent Laid-open Publication No. HEI 5-76618, proposed is to use a gas cleaning apparatus provided with a fixed-bed type solvent recovery unit having an activated carbon fiber adsorbent for adsorbing the solvent vapor sucked from the contaminated soil and a steam supply unit for regenerating, i.e. desorbing, the activated carbon fiber adsorbent. However, in such apparatus, a large quantity of regenerating steam must be utilized and a large quantity of condensed water dissolving the organic solvent is generated in the subsequent solvent separation process, namely the decantation process. Thus, such condensed water cannot be discharged as it is and a new waste water treating process or means for removing the organic solvent dissolving in the condensed water is additionally required. In such process, however, the organic solvent thus removed from the condensed water will have to be exhausted into atmosphere in many cases, which constitutes a secondary contamination problem. Furthermore, a cooling means is also required for condensing a large amount of steam, which involves a large coolant requirement.
Still furthermore, in the Japanese Patent Laid-open Publication No. SHO 52-14580, and in the U.S. Pat. Nos. 4,259,094, 4,207,082, 4,061,477 and 4,047,906, there is proposed a gas treating apparatus provided with a multistage fluidized bed type adsorption unit for cleaning a harmful substance in the atmosphere through the contact with spherical activated carbon particles and a heat desorption unit for desorbing the harmful substance from the activated carbon adsorbing the harmful substance and for regenerating the activated carbon. However, since such apparatus generally has a vertically elongated structure in which the respective units or equipments are integrally arranged in series, it is difficult to move the apparatus itself and hence difficult to utilize the apparatus in different operating sites.